Apparatus and methods for substantial planarization of solder bumps

ABSTRACT

Apparatus and methods for substantial planarization of solder bumps. In one embodiment, an apparatus includes a planarization member engageable with at least some of the plurality of outer surfaces to apply a planarization action on one or more of the outer surfaces to substantially planarize the plurality of outer surfaces, and a securing element to securely position the bumped device during engagement with the planarization member. Through application of “additive” and/or “subtractive” processes, the solder balls are substantially planarized. In alternate embodiments, the planarization member includes a cutting tool and the planarization action comprises a milling action; or the planarization member includes a heated platen and the planarization action comprises a thermo-mechanical deformation action; or the planarization member includes an abrasive surface and the planarization action comprises a grinding action; or the planarization member includes a chemical solution and the planarization action comprises a chemical reaction; or the planarization member includes a solder deposition device and the planarization action comprises a solder. In a further embodiment, an apparatus includes a load device to urge the at least some outer surfaces of the bumped device into engagement with the planarization member.

TECHNICAL FIELD

[0001] The present invention relates to apparatus and methods forsubstantial planarization of solder bumps for use in, for example,testing and fabrication of chip scale packages, bumped die, and othersimilar devices.

BACKGROUND OF THE INVENTION

[0002] The demand for smaller packaging of electronic componentscontinues to drive the development of smaller chip scale packages(CSP's), bumped die, and other similar devices having solder bumps, ballgrid arrays (BGA's), or the like. As a result, spacing (or “pitch”)between adjacent solder balls on bumped devices has steadily decreased.Typical requirements for ball pitch have decreased from 1.27 mm to 0.5mm or less, and the trend continues.

[0003]FIG. 1 is a side elevational view of a typical bumped device 10(CSP, bumped die, etc.) mounted on, for example, a printed circuit board20. The bumped device 10 includes a plurality of solder balls 12attached to a plurality of ball pads (not shown) which are formed on adie 14. Each solder ball 12 has an outer edge 16 that aligns with acorresponding contact pad 18 on the printed circuit board 20. Aconductive lead 22 is attached to each contact pad 18. Ideally, theouter edge 16 of each solder ball 12 contacts the corresponding contactpad 18 during assembly of the bumped device 10 with the printed circuitboard 20, completing the electrical circuit between the conductive leads22 and the die 14.

[0004] The height and width of the solder bumps 12 on the bumped device10 are not precisely uniform. Variation of the solder bump height andwidth depends on several factors, including variation in size of theoriginal unattached solder balls, variation in the sizes of the ballpads, and differences in the attachment process.

[0005] As the demand for smaller packaging continues, however, CSPreliability concerns arise. For example, using typical manufacturingmethods and solders, the nominal variation between the tallest andshortest balls (shown as the distance d on FIG. 1) is presently about 60microns (μm). Therefore, when the device 10 is placed on a flat surfaceresting on the solder balls, the three tallest balls or bumps define theseating plane of the device, and the smaller balls do not touch thecorresponding contact pads of the printed circuit board or testinterposer.

[0006] During assembly, and in some cases during testing, a moderatecompression force may be applied to the bumped device 10 to drive theouter surfaces 16 of the solder balls 12 into contact with the contactpads 18 of the printed circuit board or test interposer 20. Typically,the compression force needed to bring the solder bumps into contact withthe contact pads varies between 30 grams and 2000 grams depending uponthe manufacturing or test process involved. The applied compressionforce should be kept to a minimum, however, because larger forces maydamage the circuitry of the die 14, the CSP solder balls, or the testinterposer.

[0007] One approach to the problem is to mount the contact pads 18 ofthe test interposer 20 on micro-springs. As the tallest solder bumpsengage the micro-spring mounted contact pads, the micro-springs axecompressed, allowing the shorter solder balls to engage thecorresponding contact pads. Numerous micro-spring contact pad models areavailable as shown and described in Robert Crowley's article in ChipScale Review published May 1998, p. 37, incorporated herein byreference. Although desirable results may be achieved with such devices,micro-spring mounted contact pads 18 are very expensive, relativelydifficult to maintain, and may excessively damage the solder ballitself.

[0008] During assembly of the bumped device 10 with the printed circuitboard 20, some of the shorter solder balls may not solder to theirassociated contact pads during the reflow process. In the past, toincrease the numbers of solder balls making contact with the contactpads during reflow, the volume of the solder balls was increased. Aspackaging sizes and pitch requirements continue to decrease, however,the volume of the solder balls must be reduced accordingly, and thus,the percentage of balls that will not attach to the contact pads duringreflow increases. Again, if considerable force is applied duringassembly, the CSP or the printed circuit board 20 may be damaged.

SUMMARY OF THE INVENTION

[0009] The present invention is directed toward apparatus and methodsfor substantial planarization of solder bumps for use in, for example,testing and fabrication of chip scale packages, bumped die, and othersimilar devices. In one embodiment, an apparatus in accordance with theinvention includes a planarization member engageable with at least someof the plurality of outer surfaces, and a securing element engageablewith the bumped device to securely position the bumped device duringengagement with the planarization member. During engagement with the atleast some outer surfaces, the planarization member applies aplanarization action on one or more of the outer surfaces tosubstantially planarize the plurality of outer surfaces. In oneembodiment, the planarization member includes a cutting tool and theplanarization action comprises a milling action. In another embodiment,the planarization member includes a heated platen and the planarizationaction comprises a thermo-mechanical deformation action. In yet anotherembodiment, the planarization member includes an abrasive surface andthe planarization action comprising a grinding action. Alternately, theplanarization member includes a chemical solution and the planarizationaction comprises a chemical reaction. In yet another embodiment, theplanarization member includes a solder deposition device and theplanarization action comprises a solder deposition.

[0010] Alternately, an apparatus may include a planarization gauge thatmeasures a planarization condition of the outer surfaces. Theplanarization gauge may measure the planarization condition before orafter the planarization member is engaged with the outer surfaces.

[0011] In a further embodiment, an apparatus includes a load deviceengageable with at least one of the bumped device or the planarizationmember to urge the at least some outer surfaces of the bumped deviceinto engagement with the planarization member. The planarization memberapplies a planarization action on one or more of the plurality of outersurfaces to substantially planarize the plurality of outer surfaces.

[0012] In one embodiment, the planarization member includes asubstantially flat surface and the load device includes a mass having aweight that urges the at least some outer surfaces into engagement withthe flat surface to mechanically flatten the surfaces. In anotherembodiment, the load device includes a fixed surface and a pressurizablevessel, a pressure in the pressurizable vessel urging the bumped deviceaway from the fixed surface and into engagement with the planarizationmember. In yet another embodiment, the load device includes a pressengageable with the bumped device. In still another embodiment, the loaddevice includes a centrifuge engageable with the planarization member.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a side elevational view of a bumped device engaged witha printed circuit board in accordance with the prior art.

[0014]FIG. 2 is a side elevational view of the bumped device of FIG. 1engaged with a planarization apparatus in accordance with an embodimentof the invention.

[0015]FIG. 3 is a side elevational view of the bumped device engagedwith the printed circuit board of FIG. 1 following substantialplanarization of the bumps in accordance with the invention.

[0016]FIG. 4 is a side elevational view of the bumped device of FIG. 1engaged with a device having protruding contacts.

[0017]FIG. 5 is a side elevational view of the bumped device of FIG. 1engaged with a planarization apparatus in accordance with an alternateembodiment of the invention.

[0018]FIG. 6 is a side elevational view of the bumped device of FIG. 1engaged with an alternate embodiment of a planarization apparatus inaccordance with the invention.

[0019]FIG. 7 is a side elevational view of an alternate embodiment of aplanarization apparatus in accordance with the invention.

[0020]FIG. 8 is a side elevational view of another alternate embodimentof a planarization apparatus in accordance with the invention.

[0021]FIG. 9 is a side elevational view of yet another alternateembodiment of a planarization apparatus in accordance with theinvention.

[0022]FIG. 10 shows a partial cross-sectional view of still anotherembodiment of a planarization apparatus in accordance with theinvention.

DETAILED DESCRIPTION OF THE INVENTION

[0023] The following description is generally directed toward apparatusand methods for substantial planarization of solder bumps for use in,for example, testing and fabrication of chip scale packages, bumped die,and other similar devices. Many specific details of certain embodimentsof the invention are set forth in the following description and in FIGS.2-10 to provide a thorough understanding of such embodiments. Oneskilled in the art, however, will understand that the present inventionmay have additional embodiments, or that the present invention may bepracticed without several of the details described in the followingdescription.

[0024]FIG. 2 is a side elevational view of a bumped device 10 engagedwith a planarization apparatus 100 in accordance with an embodiment ofthe invention. In this embodiment, the planarization apparatus 100includes a rotating cutting head 102 with a plurality of cutting blades104. A securing element 106 having a recess 108 adapted to receive thebumped device 10 is engaged with the bumped device 10 to secure thebumped device 10 in position during engagement of the solder balls 12with the cutting head 102. A planarization gauge (or sensor) 109 ispositioned proximate the bumped device 10 to measure (or sense) aplanarization condition of the outer surfaces 16 of the solder balls 12.

[0025] As used throughout the following discussion, the term “bumpeddevice” refers not only to the bumped die depicted in FIG. 2, but alsoto a wide variety of microelectronics devices having solder bumps,including CSP's, flip-chips, ball grid array (BGA) packages, andmicro-BGA packages. Furthermore, the term bumped device is intendedherein to include multiples or combinations of bumped devices, such asan entire wafer of bumped dice prior to die singulation, or an entirehandling tray containing multiple bumped packages.

[0026] In operation, the securing element 106 secures the bumped device10 in position for engagement of the bumped device 10 with the cuttinghead 102. As the cutting head 102 is moved along the bumped device 10(or vice versa), the cutting blades 104 rotate (as indicated by arrow w)and engage the outer surfaces 16 of the tallest solder bumps 12. Thecutting blades 104 perform a planarization action (i.e. subtractivecutting or milling) on the outer surfaces 16 of one or more of the bumps12. After engagement of the bumped device 10 with the planarizationmember 100, the gauge 109 may be used to check the outer surfaces 16, 16a to determine whether the solder balls 12 are all approximately thesame height. If the outer surfaces are not planarized to the desiredtolerance, the planarization apparatus 100 may be re-engaged with theouter surfaces 16, 16 a one or more times until the balls aresubstantially planarized.

[0027] The terms “planarized” and “planarization” are used throughoutthis discussion to refer to the fact that the solder balls 12 are madeto be approximately the same height—that is to say, the solder ballsproject from the bumped device by approximately the same distance orthickness. It is not intended to imply that the outer surfaces 16 of allof the solder balls 12 are made flat. As shown in FIG. 2, theplanarization apparatus 100 need not engage all of the solder balls 12,and solder balls of different heights are engaged to different degrees.The actual number of solder balls engaged by the planarization apparatus100 will depend upon the height variation of the balls of the array.Thus, some of the outer surfaces 16 a of the solder balls 12 may beflattened, and some will remain rounded. Following application of theplanarization action, the plurality of solder balls on the bumped devicewill be substantially (i.e. approximately) the same height, a conditionreferred to as “substantially planarized.”

[0028] In an alternate embodiment, as shown in FIG. 2, a planarizationmember 100A includes a cutting tool 103 that is oriented approximatelyperpendicular to the die 14. The cutting tool 103 may be positioned on acontrollably driven base (not shown) and may be sized to apply aplanarization action on a single solder bump 12. Thus, rather thanflattening a row or group of solder bumps 12 in a batch mode, thecutting tool 103 allows individual solder balls 12 to be selected formilling. The cutting tool 103 could also be used to remove most or allof a damaged ball. The ball could then be replaced by installation of apreformed ball, or by successive deposition of layers of solder using asolder deposition process, as described more fully below.

[0029] One may note that the planarization gauge 109 is depicted in FIG.2 as being an optical device that senses the planarity of the outersurfaces 16, 16 a, such as the type of laser-based gauges disclosed inU.S. Pat. No. 5,663,797 to Sandhu for detecting the endpoint inchemical-mechanical polishing of semiconductor wafers. The gauge 109,however, may be of any type that is suitable for detecting the heightsof the solder bumps, including feeler gauges that physically contact thesolder bumps or non-contacting capacitative-type height gauges.Alternately, the planarization gauge 109 may be incorporated into eitherthe planarization member 100, 100A or the securing element 106, or byproper control of the planarization member and securing element, thegauge may be eliminated.

[0030] It should be noted that the gauge 109 could measure all the balls12 on the package 10 and then the planarization member 100, 100A couldbe directed to only mill off the “tallest” balls. The balls chosen toreceive the planarization action could be determined by, for example, asoftware program. The software program could accept input signals fromthe gauge 109 and transmit control signals to a controller whichcontrollably positions the planarization member 100, 100A to act on thetallest solder balls 12, thus substantially planarizing the solder ballsin a fully-automated, controlled fashion.

[0031]FIG. 3 is a side elevational view of the bumped device 10 engagedwith the printed circuit board 20 of FIG. 1 following substantialplanarization of the outer surfaces 16, 16 a. After engagement with theplanarization apparatus 100, most or all of the outer surfaces 16, 16 aare in contact with the corresponding contact pads 18 on the printedcircuit board 20.

[0032] An advantage of substantially planarizing the outer surfaces 16,16 a of the bumped device 10 is that testing of the die 14 issignificantly enhanced. Because the solder balls 12 are brought intocontact with the contact pads 18 with minimal applied force, reliabletesting of the die may be achieved without damaging the circuitry of thedie.

[0033] Another advantage of substantially planarizing the outer surfacesof the solder bumps is that expensive micro-spring contact devices areeliminated. Significant cost and maintenance savings may be realizedusing the relatively simple, economical planarization member comparedwith the purchase or fabrication of a test interposer havingmicro-spring mounted contact devices.

[0034] Yet another advantage is realized when the substantiallyplanarized outer surfaces 16 a are engaged with a device 20 a (e.g.printed circuit board, test interposer, etc.) having protruding orpedestal-shaped contacts 18 a. FIG. 4 shows the bumped device 10 havingsubstantially planarized solder bumps 12 engaged with a test interposer20 a having protruding contacts 18 a. Without planarization of thesolder bumps 12, the height h of the protruding contacts 18 a, wouldneed to be on the order of 60 μm—the nominal variation between thetallest and shortest balls without planarization (shown as distance d onFIG. 1).

[0035] When the outer surfaces of the solder balls are substantiallyplanarized, however, the variation of solder ball heights is reduced sothat the required pedestal contact height is reduced accordingly. Withthe solder balls substantially planarized, the required height of theprotruding contacts 18 a on the test interposer 20 a, for example, isreduced to about 20 μm, which is just enough to penetrate a layer ofsurface oxides on the solder balls for testing of the bumped device 10.By reducing the height requirement of the protruding contacts,substantial savings in manufacturing costs of the protruding contacts isachieved.

[0036]FIG. 5 is a side elevational view of the bumped device 10 of FIG.1 engaged with an alternate embodiment of a planarization apparatus 200in accordance with the invention. In this embodiment, the planarizationapparatus 200 includes a heated platen 202 having a substantially flatsurface 204 engageable with the outer surfaces 16 of the solder balls12, and a securing element 206 having an aperture 208 therethrough. Thebumped device 10 is securely engaged within the aperture 208 so that thesecuring element 206 secures and positions the device during engagementwith the heated platen 202.

[0037] As the heated platen 202 is engaged with the outer surfaces 16,the outer surfaces are heated by the flat surface 204 of the platen.Depending upon the temperature of the platen 202, and the period ofcontact with the platen, the outer surfaces may be softened andmechanically flattened by the flat surface 204, or may be heated untilthe solder sublimates. In either case, these thermo-mechanical actionsperformed by the heated platen 202 on the solder balls 12 substantiallyplanarize the outer surfaces 16 a to an approximately uniform height.

[0038] One may note that if temperature of the platen 202 is high enoughto liquify the solder, then the platen 202 is preferably made of amaterial that the solder will not wet to. Also, if the platen 202 isremoved from the ball while the ball is still in a liquid state, thenthe surface tension of the ball may cause the ball to reform into itsoriginal undesirable spherical shape. Thus, if the platen 202temperature is sufficient to liquify the solder ball 12, then after theball has been liquified and mechanically reformed, it is preferable thatthe platen 202 temperature be reduced while the platen remains incontact with the ball 12 until the solder ball solidifies into asubstantially planarized shape.

[0039] Although the heated platen 202 is shown in FIG. 5 as onlycontacting four of the solder balls 12, it is apparent that the platenmay be made as large or as small as desirable. The platen may, forexample, be coextensive with all the balls of the bumped device 10.Alternately, the heated platen may be configured to contact only oneball (or one row) at a time, such as by using a roller, a blade, asqueegee, or other configuration.

[0040] Numerous alternate embodiments of planarization apparatus areconceivable. For example, in one alternate embodiment, the planarizationapparatus 200 includes a grinding member 202 having an abrasive surface204 engageable with the outer surfaces 16 of the solder bumps 12. Inthis embodiment, the grinding member 202 is laterally moveable(indicated in FIG. 4 by the double-headed arrow h) with respect to thesolder bumps 12. As the grinding member 202 is moved, the abrasivesurface 204 performs a grinding action on one or more of the bumps 12,thereby substantially planarizing the outer surfaces 16 a.

[0041] Alternately, the grinding member may rotate with respect to thebumps in a manner similar to the chemical-mechanical polishing (CMP)devices for planarization of silicon wafers, including, for example, thetypes disclosed in U.S. Pat. No. 5,738,567 to Manzonie and Akram. Theabrasive surface 204 may be used with a polishing solution that helps todissolve the outer surfaces of the solder bumps, or an abrasive slurrythat assists in the physical removal of material from the outersurfaces. Furthermore, planarization apparatus in accordance with theinvention may be used to planarize the solder balls of flip-chip deviceswhile still in whole wafer form, prior to die singulation of the wafer.

[0042] In another alternate embodiment, the planarization apparatus 200includes a reactive member 202 having a chemically-coated or wettedsurface 204. As the wetted surface 204 is engaged with the outersurfaces, a chemical action is performed on the solder bumps whichdissolves the outer edges of the tallest bumps, making the bumpsapproximately the same height and substantially planarizing the outersurfaces 16, 16 a. Suitable chemicals for coating or wetting the surface204 for chemically reacting with the solder balls are known in theindustry, as discussed in greater detail below. Many alternateembodiments of securing elements are available, including, for example,those having recesses (FIG. 1), apertures (FIG. 2), pinching mechanisms,clamping mechanisms, or suction mechanisms. In general, all types ofsecuring elements that securely position the bumped device duringengagement with the planarization member are acceptable.

[0043]FIG. 6 is a side elevational view of the bumped device 10 of FIG.1 engaged with an alternate embodiment of a planarization apparatus 300in accordance with the invention. In this embodiment, the planarizationapparatus 300 has a pair of contact posts 302 that contact the outersurfaces 16 of the solder balls 12, and a solder deposition device 304.The solder deposition device 304 deposits a solder buildup layer 308 onselected solder balls 12. A securing element 306 pinches the substrate14 of the bumped device 10 to securely position the device duringengagement with the solder deposition device 304.

[0044] In operation, the contact posts 302 systematically contact theouter surfaces 16 of at least some of the solder balls 12 to determinethe highest solder balls 12. The highest solder balls then define aseating plane 307. For example, for a two-dimensional array of solderballs, the seating plane 307 may be defined by the three tallest ballsor, if desired, from the single tallest ball. Similarly, for a singlerow of solder balls, the seating plane 307 may be determined from thetwo tallest balls or the single tallest ball. Once the seating plane 307is established, the solder deposition device 304 is positioned over eachof the shorter solder balls and deposits one or more buildup layers ofsolder 308 on each of the shorter balls. The buildup layers 308 aresuccessively applied until the height of each solder ball reaches theseating plane 307 through an “additive” planarization process, and theouter surfaces are substantially planarized.

[0045] One may note that the process involving definition of the seatingplane 307 may be employed equally well with the planarization apparatusthat employ “substractive” planarization actions, such as the rotatingcutter or the heated platen. Furthermore, through combination of various“substractive” and “additive” processes, damaged balls may be partiallyor wholly removed and replaced until the solder balls 12 aresubstantially planarized. Thus, the inventive apparatus and processesmay be used to rework or repair bumped devices 10 with missing ordamaged solder balls.

[0046] Although the planarization apparatus 300 is shown in FIG. 6 ashaving two contact posts 302, it should be recognized that manyalternative ways of defining the seating plane 307 exist. For example,the planarization apparatus 300 may have only a single contact post thatis used to sample the heights the solder bumps, or may have a contactpost for each of the solder bumps on the bumped device 10.

[0047] Also, the planarization apparatus 300 may have a single,adjustably positionable solder deposition device 304 as shown in FIG. 6,or many solder deposition devices, such as one solder deposition deviceper solder bump. The solder deposition device 304 may include a solderjet, or a solder ball bumper, or other suitable device. Representative,commercially-available devices include the drop-on demand solder jetsystems from MPM Corporation of Franklin, Mass., or the solder ballbumper Model SB²M from Packaging Technologies, GmbH of Germany.

[0048] It may also be noted that the seating plane 307 may be defined atany desired intermediate level that is somewhere between the highest andlowest bumps. In that case, the solder deposition device 304 could beused to build up the heights of the shorter solder bumps 12, whileanother planarization member (e.g. cutting head, heated platen, etc.)could be used to reduce the heights of the taller solder bumps until allof the solder bumps are substantially planarized.

[0049]FIG. 7 is a side elevational view of an alternate embodiment of aplanarization apparatus 400 in accordance with the invention. Thisembodiment of the planarization apparatus 400 is suitable for use with,for example, a bumped device 10 a that is capable of withstanding amoderate or larger compression load without sustaining damage. Theplanarization apparatus 400 includes a planarization chuck 402 having asubstantially flat surface 404, and a retaining mass 406 engaged withthe substrate 14 of the bumped device 10 a.

[0050] In operation, the bumped device 10 a is positioned with thesolder balls 12 facing the flat surface 404 of the planarization chuck402, and the retaining mass 406 is engaged onto the bumped device, 10 a.The retaining mass 406 secures the bumped device 10 a into engagementwith the planarization chuck 402, and the weight of the retaining mass406 compresses the solder balls 12 against the flat surface 404,flattening the outer surface 16 of some or all of the balls,particularly the tallest balls. The compression caused by the weight ofthe retaining mass mechanically deforms the outer surfaces 16 a, therebysubstantially planarizing the outer surfaces 16, 16 a of the solderballs. Thus, the planarization member 400 advantageously provides thebenefits of substantial planarization of the solder balls using asimple, inexpensive, and easily maintainable system.

[0051] It should be noted that the compression force that flattens theouter surfaces 16 a of the solder balls can be generated in manydifferent ways. FIG. 8, for example, shows an alternate embodiment of aplanarization apparatus 500 having a pressure plate 532 engaged againstthe bumped die 10 a opposite from the planarization chuck 402. Apressurizable vessel 534 is positioned above the pressure plate 532, anda fixed wall 536 is positioned over the pressurizable vessel 534. As thepressurizable vessel 534 is inflated, the pressure in the vessel forcesthe pressure plate 532 downward against the bumped die 10 a, compressingthe solder balls 12 against the flat surface 404 and flattening theouter surfaces 16 a.

[0052] In another embodiment, the pressure plate 532 is removed, and thepressurizable vessel 534 engages the bumped die 10 a directly to applythe compression force. Alternately, the compression force could begenerated by any number of devices which are commonly known in theindustry, including, for example, a press, a motor and mechanicallinkage, or other devices.

[0053]FIG. 9 is a side elevational view of yet another embodiment of aplanarization apparatus 600 in accordance with the invention. In thisembodiment, the planarization apparatus 600 includes a planarizationchuck 602 having a substantially flat surface 604, and a centrifuge 610.A pair of securing members (or clips) 606 engage and secure the bumpeddevice 10 a in position on the planarization chuck 602 with the solderballs 12 of the bumped device 10 a engaged with the flat surface 604. .

[0054] In operation, the centrifuge 610 is rotated as depicted by arrowR. The rotation of the centrifuge generates a centrifugal force thatcompresses the bumped device 10 a against the planarization chuck 602.During acceleration (and deceleration) of the centrifuge 610, thesecuring members 606 secure the bumped device 10 a in position on theplanarization chuck 602. As the rotational velocity of the centrifuge610 increases, a centrifugal force begins to press some or all of thesolder bumps 12 into the flat surface 604, substantially flattening theouter surfaces 16 a against the flat surface 604. As shown in FIG. 8,one or more planarization chucks 602 may be disposed within thecentrifuge 610 for simultaneously planarizing more than one bumpeddevice 10 a. The centrifuge 610 advantageously eliminates the use ofweights, pressurization vessels, or other devices used to generate thecompression force.

[0055]FIG. 10 shows a partial cross-sectional view of still anotherembodiment of a planarization apparatus 700 in accordance with theinvention. In this embodiment, the planarization apparatus 700 includesa receptacle 702 having a retaining wall 704. The retaining wall 704partially encloses a receiving space 706 that is sized to receivablyengage the bumped device 10. With the bumped device 10 placed in aninverted position within the receiving space 706, the retaining wall 704projects above the outer surfaces 16 b of the tallest solder bumps 12(shown in dashed lines). A protective layer 740 is disposed on thebumped device 10 within the receiving space 706, the protective layer740 at least partially surrounding and encasing the solder bumps 12. Theprotective layer 740 includes an upper surface 707. A reactive solution750 is disposed within the receiving space 706 on the upper surface 07of the protective layer 740, and a planarization gauge 109 is positionedproximate the receptacle 702.

[0056] In operation, the protective layer 740 is formed so that itsthickness is approximately equal to the height of the shortest solderbump 12. The upper surface 707 thereby defines a seating plane throughwhich the outer surfaces 16 b project. The reactive solution 750 is thendeposited into the receiving space 706 to chemically react with anddissolve (i.e. etch) the outer surfaces 16 b of the solder bumps 12. Theprotective layer 740 is comprised of one or more materials that areresistive or inert to the reactive solution 750. As the reactivesolution 750 etches the projecting portion of the outer surfaces 16 b,the planarization gauge 109 monitors a planarization condition of theseating plane and outer surfaces (as discussed above). When the outersurfaces 16 a are substantially planar with the upper surface 707, thereactive solution 750 is removed. The protective layer 740 is thenetched or dissolved using a suitable solution or other process (e.g. byheating) that removes the protective layer but does not harm the solderbumps 12. The heights of the solder bumps 12 on the bumped device 10 arethereby substantially planarized.

[0057] Suitable reactive solutions 750 for etching the solder balls 12are known, and include, for example, ammonium bifluoride/peroxide,nitric/ferric nitrate acid, nitric/hydrofluoric acid, or a two-stepcombination of nitric acid followed by ferric chloride. Similarly,suitable materials for the protective layer 740 are widely known.

[0058] The planarization gauge 109 could be incorporated into thereceptacle 702, such as by being disposed within the retaining wall 704.Alternately, by proper control or calibration of the reactive solution750 and/or the solder composition, the planarization gauge 109 may beeliminated.

[0059] In an alternate embodiment, the bumped device 10 is re-positionedwith the solder bumps 12 projecting downwardly, and the reactivesolution 750 is contained in a vat or reservoir below the bumped device10. Using a suitable securing element, the bumped device 10 could becontrollably lowered (or the reservoir of reactive solution raised)until some or all of the outer surfaces 16, but at least the outersurfaces 16 b of the tallest solder bumps, come into contact with thereactive solution 750. The reactive solution 750 then etches anddissolves the outer surfaces that come into contact with the reactivesolution, dissolving the outer surfaces and substantially planarizingthe solder bumps.

[0060] In this embodiment, the protective layer 740, the retaining wall704, and the planarization gauge 109 may be eliminated. Thus, thebenefits of substantial planarization of the solder balls 12 areachieved using a relatively simple, easily maintainable planarizationsystem.

[0061] The above-described embodiments of planarization apparatus, andtheir equivalents, provide improved testing, manufacture, and packagingof bumped devices by substantially planarizing the outer surfaces of thesolder balls. By substantial planarization of the solder bumps, thecompression forces needed to engage the solder balls 12 into contactwith the contact pads 18 or a test interposer, printed circuit board, orother bumped device are substantially reduced or eliminated, therebyimproving reliability and avoiding damage to the bumped device.Expensive alternatives, such as micro-spring contact pads, areeliminated. Another advantage is that substantial planarization of thesolder balls improves the engagement of the bumped device with a devicehaving pedestal or protruding contacts, simplifying the manufacturingand reducing the cost of such devices.

[0062] The detailed descriptions of the above embodiments are notexhaustive descriptions of all embodiments contemplated by the inventorto be within the scope of the invention. Indeed, persons skilled in theart will recognize that certain elements of the above-describedembodiments may variously be combined or eliminated to create furtherembodiments, and such further embodiments fall within the scope andteachings of the invention. It will also be apparent to those ofordinary skill in the art that the above-described embodiments may becombined in whole or in part to create additional embodiments within thescope and teachings of the invention.

[0063] Thus, although specific embodiments of, and examples for, theinvention are described herein for illustrative purposes, variousequivalent modifications are possible within the scope of the invention,as those skilled in the relevant art will recognize. The teachingsprovided herein of the invention can be applied to other apparatus andmethods for substantial planarization of solder bumps, and not just tothe apparatus and methods described above and shown in the figures. Ingeneral, in the following claims, the terms used should not be construedto limit the invention to the specific embodiments disclosed in thespecification and the claims, but should be construed to include allapparatus and methods that operate under the claims to providesubstantially planarized solder bumps. Accordingly, the invention is notlimited by the foregoing disclosure, but instead its scope is to bedetermined by the following claims.

1. An apparatus for substantially planarizing a plurality of outer surfaces of an array of solder bumps attached to a bumped device, comprising: a planarization member engageable with at least some of the plurality of outer surfaces, the planarization member applying a planarization action on one or more of the plurality of outer surfaces to substantially planarize the solder bumps; and a securing element engageable with the bumped device to securely position the bumped device during engagement of the planarization member with the outer surfaces.
 2. The apparatus of claim 1 , further comprising a planarization gauge engageable with at least a portion of the outer surfaces to assess a planarization condition of the solder bumps.
 3. The apparatus of claim 1 wherein the planarization member includes a cutting tool and the planarization action comprises a milling action on the one or more outer surfaces.
 4. The apparatus of claim 1 wherein the planarization member includes a heated platen and the planarization action comprises a thermo-mechanical deformation action on the one or more outer surfaces.
 5. The apparatus of claim 1 wherein the planarization member includes an abrasive surface and the planarization action comprises a grinding action on the one or more outer surfaces.
 6. The apparatus of claim 1 wherein the planarization member includes a chemical solution and the planarization action comprises a chemical reaction with the one or more outer surfaces.
 7. The apparatus of claim 1 wherein the planarization member includes a solder deposition device and the planarization action comprises a solder deposition on the one or more outer surfaces.
 8. The apparatus of claim 7 , further comprising a contact member engageable with one or more of the solder bumps to determine a seating plane, the solder deposition device applying the solder deposition on the one or more outer surfaces until the outer surfaces are substantially planarized along the seating plane.
 9. The apparatus of claim 1 wherein the securing element includes a retaining wall sized to define a receiving space for receiving the bumped device, further comprising a protective layer disposed within the receiving space and at least partially covering the solder bumps except for the one or more outer surfaces, and wherein the planarization member includes a reactive solution disposed within the receiving space on the protective layer, the planarization action comprising an etching of the one or more outer surfaces by the reactive solution.
 10. The apparatus of claim 1 wherein the planarization member includes a reservoir of a reactive solution and the securing element securely positions the bumped device with the solder bumps projecting downwardly toward the reservoir, the planarization action comprising an etching of the one or more outer surfaces by the reactive solution when the one or more outer surfaces are brought into contact with the reactive solution.
 11. The apparatus of claim 1 wherein the at least some outer surfaces engageable by the planarization member include the one or more outer surfaces upon which the planarization action is applied.
 12. The apparatus of claim 1 wherein the securing element includes a retaining mass positioned on the bumped device and the planarization member includes a substantially flat surface positioned below the bumped device in contact with the at least some outer surfaces, the planarization action comprising a compressive force due to the weight of the retaining mass, the compressive force mechanically flattening the one or more outer surfaces.
 13. The apparatus of claim 1 , further comprising a load device engageable with at least one of the bumped device or the planarization member to urge the at least some outer surfaces of the bumped device into engagement with the planarization member.
 14. The apparatus of claim 13 wherein the load device includes a fixed surface and a pressurizable vessel disposed between the fixed surface and the bumped device, a pressure in the pressurizable chamber urging the bumped device away from the fixed surface and into engagement with the planarization member.
 15. The apparatus of claim 13 wherein the securing element includes a retaining clip engageable with a substrate of the bumped device and the planarization member includes a substantially flat surface in contact with the at least some outer surfaces, the load device including a centrifuge engageable with the planarization member, the planarization action comprising a centrifugal force that compresses and mechanically flattens the one or more outer surfaces against the flat surface.
 16. An apparatus for approximately planarizing a plurality of solder bumps, comprising: a planarization member engageable with at least some of the plurality of solder bumps to apply a planarization action on one or more of the plurality of solder bumps to approximately equalize the heights of the solder bumps on a bumped device; and a securing element engageable with the bumped device to securely position the bumped device during engagement of the planarization member with the solder bumps.
 17. The apparatus of claim 16 , further comprising a planarization gauge engageable with at least a portion of the solder bumps to assess a planarization condition of the solder bumps.
 18. The apparatus of claim 16 , further comprising a load device engageable with at least one of the planarization member or the bumped device to urge the at least some solder bumps into engagement with the planarization member.
 19. A method of substantially planarizing an array of solder bumps attached to a bumped device, comprising: securely positioning the array of solder bumps proximate a planarization member; engaging the planarization member with at least some of a plurality of outer surfaces of the solder bumps; and applying a planarization action with the planarization member to one or more of the outer surfaces to substantially planarize the array of solder bumps.
 20. The method of claim 19 , further comprising sensing at least some of the plurality of outer surfaces to define a seating plane.
 21. The method of claim 19 , further comprising gauging a planarization condition of the array of solder bumps.
 22. The method of claim 21 wherein gauging a planarization condition of the array of solder bumps comprises gauging the planarization condition of the array of solder bumps after engaging the planarization member with at least some of the plurality of outer surfaces of the solder bumps.
 23. The method of claim 19 wherein the planarization member has a substantially flat surface and applying a planarization action with the planarization member to one or more of the outer surfaces comprises applying a compressive force with the substantially flat surface to mechanically flatten the one or more outer surfaces.
 24. The method of claim 19 wherein the planarization member includes a heated platen and applying a planarization action with the planarization member to one or more of the outer surfaces comprises at least partially thermo-mechanically deforming the one or more outer surfaces with the heated platen.
 25. The method of claim 19 wherein the planarization member includes a cutting tool and applying a planarization action with the planarization member to one or more of the outer surfaces comprises milling the one or more outer surfaces with the cutting tool.
 26. The method of claim 19 wherein the planarization member includes a chemically reactive solution and applying a planarization action with the planarization member to one or more of the outer surfaces comprises dissolving the one or more outer surfaces with the chemically reactive solution.
 27. The method of claim 19 wherein applying a planarization action with the planarization member to one or more of the outer surfaces comprises applying a planarization action with the planarization member to the at least some outer surfaces engaged with the planarization member.
 28. The method of claim 19 , further comprising engaging a load member with at least one of the bumped device or the planarization member to urge the at least some outer surfaces into engagement with the planarization member.
 29. The method of claim 19 , further comprising forming a protective layer at least partially surrounding the solder bumps.
 30. A method of substantially planarizing an array of solder bumps attached to a bumped device, comprising adjusting the thickness of at least some of the solder bumps so that all of the solder bumps in the array project from the bumped device by substantially the same distance.
 31. The method of claim 30 , further comprising securing the position of the bumped device during engagement of the planarization member with the at least some solder bumps.
 32. The method of claim 30 , further comprising gauging a planarization condition of the array of solder bumps.
 33. The method of claim 30 wherein adjusting the thickness of at least some of the solder bumps comprises milling the at least some solder bumps with a cutting tool.
 34. The method of claim 30 wherein adjusting the thickness of at least some of the solder bumps comprises thermo-mechanically deforming the at least some solder bumps.
 35. The method of claim 30 wherein adjusting the thickness of at least some of the solder bumps comprises grinding the at least some solder bumps with an abrasive.
 36. The method of claim 30 wherein adjusting the thickness of at least some of the solder bumps comprises dissolving a portion of the at least some solder bumps with a chemical solution.
 37. The method of claim 30 wherein adjusting the thickness of at least some of the solder bumps comprises mechanically flattening the at least some solder bumps.
 38. The method of claim 30 wherein adjusting the thickness of at least some of the solder bumps comprises depositing a volume of solder on the at least some solder bumps.
 39. A bumped device having an array of substantially planarized solder bumps created by a method comprising: securely positioning the array of solder bumps proximate a planarization member; engaging the planarization member with at least some of a plurality of outer surfaces of the solder bumps; and applying a planarization action with the planarization member to one or more of the outer surfaces to substantially planarize the array of solder bumps.
 40. The bumped device of claim 39 wherein the method further comprises gauging a planarization condition of the array of solder bumps.
 41. The bumped device of claim 39 wherein applying a planarization action with the planarization member to one or more of the outer surfaces comprises milling the one or more outer surfaces with a cutting tool.
 42. The bumped device of claim 39 wherein applying a planarization action with the planarization member to one or more of the outer surfaces comprises thermo-mechanically deforming the one or more outer surfaces with a heated tool.
 43. The bumped device of claim 39 wherein applying a planarization action with the planarization member to one or more of the outer surfaces comprises grinding the one or more outer surfaces with an abrasive.
 44. The bumped device of claim 39 wherein applying a planarization action with the planarization member to one or more of the outer surfaces comprises dissolving a portion of the one or more outer surfaces with a reactive solution.
 45. The bumped device of claim 39 wherein applying a planarization action with the planarization member to one or more of the outer surfaces comprises mechanically flattening the one or more outer surfaces.
 46. The bumped device of claim 39 wherein applying a planarization action with the planarization member to one or more of the outer surfaces comprises depositing a volume of solder on the one or more outer surfaces. 